The document FR 2 653 885 discloses a flow cytometry system comprising:                a measuring cell delimiting at least partially a measuring chamber,        an injection device arranged to inject a flow of biological particles to be analyzed in the measuring chamber, the injection device comprising:        an injection nozzle delimiting an internal chamber and comprising an injection orifice fluidly connected to the measuring chamber,        a first feeding conduit opening into the internal chamber and intended to feed the internal chamber with a liquid sample containing the biological particles to be analyzed in suspension, and        a second feeding conduit opening into the internal chamber and intended to feed the internal chamber with a first sheathing fluid, the injection nozzle and the second feeding conduit being configured so that the first sheathing fluid introduced in the internal chamber is capable of hydro-dynamically sheathing the liquid sample introduced in the internal chamber,        an evacuation device arranged to evacuate outside of the flow cytometry system the flow of biological particles injected in the measuring chamber, and        a measuring set arranged to measure at least one optical property of the biological particles to be analyzed, the measuring set including:        an emission device arranged to emit a light beam in the direction of the measuring chamber and capable of crossing the flow of biological particles, the emission device comprising a light source arranged to generate the light beam, and        a collecting device arranged to collect light rays coming from the measuring chamber, and more particularly light rays diffused or diffracted by each biological particle introduced in the measuring chamber and crossing the light beam.        
The hydrodynamic sheathing of the liquid sample containing the biological particles to be analyzed allows stretching the liquid sample before its passage through the injection orifice, and therefore allows, on the one hand, confining the biological particles accurately and, on the other hand, optimizing the centering of the flow of biological particles in the measuring chamber. Thus, these arrangements allow facilitating the relative positioning of the incident light beam and of the flow of biological particles, and therefore allow improving the quality of the measurements of the optical properties of the biological particles to be analyzed.
Furthermore, the flow cytometry system described in the document FR 2 653 885 allows limiting the consumption of reaction liquids because of the small volume of the measuring chamber delimited by the measuring cell.
Nonetheless, such a flow cytometry system requires the use of onerous and complex adjusting systems to align the incident light beam on the flow of biological particles.
In addition, the adjusting systems used for such a flow cytometry system present an insufficient accuracy. Thus, the optical measurements carried out with such a flow cytometry system may be improved further.